The aim of this cluster is to elaborate theoretical tools for implementing the research strategy and to develop theory that allows to specify the relationships between network characteristics, solidarity, and inequality. More specifically, research in this cluster addresses two sets of topics and problems.

The first of these revolves around the development of micro models of behavior that are suited for the study of how social contexts shape behavior and how behavior generates social phenomena and transforms the context itself. While the idea of purposive behavior constitutes a common core, a wide variety of micro models is developed and applied in ICS research. They include standard rational choice models for decision making under certainty and risk (utility theory) as well as in strategic situations (game theory) and in collective decision making. Alternative and complementary models focus on constraints for purposive behavior due to limitations of available information and information processing as well as cognitive selection processes that define or frame the action situation. Attention is paid also to models incorporating more complex motivational assumptions, such as social orientations and distributional preferences; and to bounded rationality, using learning or imitation models and evolutionary explanations. Hypotheses are generated using analytical approaches as well as simulation. An important feature of ICS research on micro models is that it takes into account the trade-off between descriptive adequacy with respect to regularities of human behavior and the underlying cognitive as well as motivational processes on the one hand, and on the other hand analytical tractability when it comes to macro-micro-macro transitions which are required given the focus on social phenomena as the explananda.

A second set of topics in this cluster is related to the development of theoretical tools for the analysis of the relationships between networks, solidarity, and inequality. Social networks can be conceived as social capital. Actors with more (and better) social capital will better achieve their goals, and purposive action will thus include investments in relations with others with an eye to expected future returns of such investments. Given a social capital approach, major problems to be addressed are, first, network effects on characteristics of actors (including abilities and attitudes) and their behavior, and social phenomena resulting from this behavior. These problems include the questions how contextual conditions such as institutional regulations affect network characteristics and the social capital associated with networks (e.g., dense networks may constitute valuable social capital under some conditions while occupying a structural hole position may be advantageous in other contexts); how network characteristics contribute to unequal distributions of social capital between different (groups of) actors and thus to social inequality; how networks affect solidarity; and when social networks have negative consequences for individuals (e.g., due to negative interdependencies or to overinvestment). The mechanism approach to explanation avoids an exclusive focus on effects of networks, and generates questions also about how networks arise, evolve, and decay. Thus, the feedback between and the dynamics of individual behavior and network structure will be studied. The social capital approach represents an instrumental perspective on networks - networks are conceived as instruments for human goal pursuit. Another approach to network formation and evolution, which will also be explored, compared, and possibly combined with the social capital approach, focuses on cognitive processes that steer social categorization and the formation of relationships through framing.